2 Los Alamos National Laboratory An unarmed Minuteman III ICBM is launched out of a silo during a test at Vandenberg Air Force Base, California. (Photo: U.S. Air Force)

DETONATION FROM THE BOTTOM UP

Joseph Martz, a technical staff member at Los Alamos since the 1980s, has held a variety of positions during his 20 years in the Lab’s Weapons Program. His responsibilities have included leadership of the pit technology group, management of enhanced surveillance in the Stockpile Stewardship Program, leadership of the weapon design division, and project head for the Reliable Replacement Warhead. NSS asked Martz for his thoughts on stockpile stewardship and its evolution over the last two decades.

Stockpile stewardship is a topic dear to my heart. I’ve been fascinated by it, and I’ve lived it—mostly on the technical side but also on the policy side. From 2009 to 2010 at Stanford University, I was a visiting scholar and the inaugural William J. Perry Fellow, working with Perry, former secretary of defense, and Sig Hecker, former Los Alamos Lab director (1986–1997). Together we looked at nuclear deterrence, nuclear policy, and stockpile stewardship and at where all this was headed. The Nuclear World Changes In my career, the years from 1989 to 1992 were the most consequential period with respect to nuclear weapons. Three very important things happened during those years, and they led to profound changes in U.S. nuclear policy. First, we had the fall of the Soviet Union, presaged by the fall of the Berlin Wall in 1989. The USSR dissolved on December 25, 1991, and the collapse of the USSR changed everything. The Cold War and its nuclear arms race were over, making an anachronism of MAD [Mutual Assured Destruction], the policy whereby, to deter nuclear war, the United States and the Soviet Union each deployed enough nuclear weapons to ensure the complete destruction of the other. Second, in 1989 the government halted work at the Rocky Flats Plant, outside of Denver, Colorado, where plutonium pits for primaries [the nuclear triggers for thermonuclear weapons] were produced. That turned out to be a seminal moment in the history of the nuclear weapons complex because, frankly, it ended our ability to produce new weapons and effectively shut down the entire nuclear weapons production complex! Over the next 10 years, more than 50 percent of the historic nuclear weapons complex was shuttered forever. Third, the Soviet Union had proposed a moratorium on nuclear testing and conducted its last test on October 24, 1990. “Divider,” conducted on September 23, 1992, was the United States’ last nuclear test. Shortly thereafter a moratorium on testing was legislatively mandated and has been followed by the United States.

National Security Science July 2014 3 designers’ skills is vital because although the Cold War is over, shifts in global politics have engendered new national security needs such as protecting the weapons with enhanced security measures in the post-9/11 world. How were we going to manage an aging stockpile and remain agile in the face of changing national security needs?

Inventing “Science-Based” Stewardship After the collapse of the Soviet Union, President Bill Clinton commissioned the first Nuclear Posture Review to examine the role of nuclear weapons in a post-Soviet world. This review (and every review since) reaffirmed the continued need for U.S. nuclear deterrence, while also recognizing the changing conditions and constraints in the global security environment. For itself and its allies, the United States would continue to maintain its nuclear stockpile, and nuclear deterrence would remain a central element of our supreme national security posture. But that presented the nuclear weapons laboratories with a huge technical challenge. How could the nuclear weapons labs ensure that nuclear weapons remained safe, secure, and reliable in the absence of nuclear testing? The question was particularly important because the weapons were going to enter configurations that we had no experience with; that is, because we weren’t continuing production, the weapons we had would, by default, age beyond their design life. Could we and our allies rely on these complicated weap- ons in spite of their aging? We would have to understand how age affected the weapons’ performance, safety, and security and do that without any further nuclear testing. The1989 fall of the Berlin Wall was the beginning of the end of the Cold War. (Photo: Open source) This also meant finding new ways to train next-generation designers without the live tests the first generation had used. Any one of those changes would have radically altered how the Lab carried out its national security mission, but all three events together put the Lab in unprecedented territory: How could we and our allies rely instead of designing and engineering new weapons for the on these aging weapons in the absence nuclear stockpile, it would now maintain the stockpile. But the cessation of nuclear testing meant the loss of the most of further nuclear testing? important tool the weapons designers had used for 50 years to develop nuclear weapons and to ensure that the stockpile Rethinking Mission “How To’s” was safe, secure, and reliable. Clearly, we had to rethink the entire problem of meeting our national security mission. Leading that process was Vic Reis, Between 1989 and 1992, three who at that time was assistant secretary for the Department events put Los Alamos in of Energy (DOE) Defense Programs. He would be assisted by the directors of the three DOE weapons laboratories. unprecedented territory. The lab directors, with Reis’s guidance, convened technical experts from across the DOE weapons complex, and what the In addition to closing the factories and putting a moratorium experts came up with was the realization that maintaining the on testing, we’d also agreed not to develop new weapons. stockpile would require an approach that was the complete That meant we’d lose the means that, along with nuclear inverse of the one used during testing. I’ll explain what testing, had developed and maintained the skills of weapons that means. designers: the continued design and production of new, upgraded nuclear weapons. However, maintaining the Continued on p. 6

4 Los Alamos National Laboratory Nuclear Weapons 101

Nuclear weapons are complex devices operating at the Modern Thermonuclear Weapon extremes of physics, chemistry, and materials science. The temperature, pressure, velocity, density, and energy Radiation Case produced in a nuclear detonation are essentially unprecedented in human experience. Furthermore, the need to ensure the safety and security of nuclear devices leads to a great paradox: the weapon must be designed to ensure that its exceptional destructive Primary Secondary power does not manifest itself when not desired but always does when required. And all the components that produce both results must be designed to fit Reentry vehicle within a volume and mass of material smaller than a kitchen stove. Imploding Primary Chemical A nuclear detonation can be viewed as a series of explosive cascading, compounding events, each of which helps amplify energy production for use in the next main stage. A modern thermonuclear weapon has two main stages: the primary and the secondary. The primary is essentially a fission bomb that releases energy from a Plutonium pit runaway fission chain reaction. That energy reaches

the secondary, setting it off. The fuel in the secondary Implosion undergoes both fission and thermonuclear fusion and releases hundreds to thousands of times more energy than a fission bomb does. Detonation of a modern thermonuclear weapon begins with an electrical signal to the primary, a signal that is scrupulously controlled to ensure it is transmitted only when there is certainty that a detonation is desired. This signal fires detonators in the primary that ignite a small charge of explosives, which in turn ignites the primary’s main charge of explosives. The symmetrical detonation of this main charge is essential for compressing a pit of fissile material—material capable of undergoing nuclear fission—into a supercritical mass. Plutonium and uranium are the fissile materials most often used to make pits. When the pit is compressed into a supercritical mass, a runaway fission chain reaction takes off, generating tremendous amounts of energy very rapidly. The energy from the primary is manifested as radiation, such as x-ray and neutron radiation. This radiation heats the weapon to temperatures exceeding the temperature of the sun. In modern, two-stage thermonuclear weapons, the primary’s radiation is reflected from the radiation case onto the secondary, a component containing both fission and fusion fuels. The tremendous amount of radiation energy absorbed by the secondary creates a crushing shock wave that compresses the secondary into a state that produces vast amounts of fission, fusion, and radiation energy. The yield from the secondary greatly exceeds what the primary can create. In an atmospheric detonation, the vast amount of radiation energy is absorbed by the air, creating a fireball that emanates thermal radiation and a tremendous shock wave, the sources of the direct damage from a nuclear explosion. Other effects of the nuclear detonation include direct radiation, both x-rays and neutrons, as well as nuclear fallout in the form of fission products.

National Security Science July 2014 5 The Rocky Flats Plant near Denver, Colorado, opened in 1952 to build plutonium pits for primaries, the triggers for thermonuclear weapons. Rocky Flats made thousands of pits per year in a plant with over 300,000 square feet of laboratory space. Pit production was temporarily halted in 1989 and completely discontinued in 1992. (Photo: Open Source) Continued from p. 4 From the Bottom Up We quickly realized the best way to do this was to represent all this basic science as a series of mathematical models and Nuclear testing was a wonderful tool. It was also the world’s then integrate all those models, along with copious amounts biggest shortcut. It meant that we didn’t have to understand of data about physical properties, into a huge computer all the details of a nuclear weapon and how it functions. (See calculation that would accurately predict a weapon’s “Nuclear Weapons 101.”) During the nuclear testing era, we performance. knew enough about how things work and how materials behave to configure a device and make a prediction as to how To be sure the calculation was accurate, we would validate it it would perform. We then detonated it to see if it worked. by comparing its results with the data from past U.S. nuclear It usually did, but sometimes it didn’t, and we didn’t always tests [over 1,000 of them] and the data from newly conducted understand why. Basically, we solved the problem of building “integrated” experiments. Integrated experiments reproduce safety, security, and reliability into a weapon from the top in the real world some portion of how weapons perform, for down: if the full device worked, its components must be working. So we froze the design at this point and did our best to build systems that exactly replicated what we had tested.

Stockpile stewardship is all about doing nuclear testing on a computer. It’s just damn hard on the computer!

In the post-testing era, we realized that without the top-down approach, we would have to piece together how nuclear weapons function from the bottom up—that is, gather all the basic science pieces underlying the behavior of each of the weapons’ different materials and physical processes and then A gas gun at Los Alamos sends projectiles into targets at high speeds so use that information to calculate how the complete nuclear scientists can study the properties of plutonium and other weapons materials weapon would function. at high shock pressur­ es, temperatures, and strain rates. (Photo: Los Alamos)

6 Los Alamos National Laboratory example, how some configuration of materials in a warhead how those properties changed under extreme pressures, behaves when hit by shock waves during detonation. Thus, temperatures, forces, and accelerations, especially after the integrated tests would put real-world checks and balances on materials aged. our virtual-world calculations of performance. In the nuclear testing era, we’d never thoroughly character- This was the bottom-up approach. It would enable weapons ized the properties of the materials that went into the weap- designers to make technically sound judgments about a ons—we hadn’t needed to because the weapons were tested weapon’s performance without any new nuclear tests. In 1994, and regularly replaced. This limited characterization was no shortly after its conception, we named this approach “science- more evident than for the most important material in the based stockpile stewardship,” now the Stockpile Stewardship weapon: plutonium. Program. A colleague of mine, Jas Mercer-Smith, has a good For example, we didn’t understand the details of how the line about this. He likes to say, “Stockpile stewardship is all plutonium sphere [the “pit” inside the primary of a nuclear about doing nuclear testing in a computer. It’s just damn hard weapon] gets compressed when its surface is hit by a strong on the computer!” shock wave from high explosives. The pressure from the shock wave causes the plutonium not only to implode [move inward] but also to get denser because the atoms in the Finding the Fundamental Science Pieces plutonium are forced closer together [compressed]. But how We realized in the early 1990s not only that computer calcu- much pressure causes how much compression, that is, how lations of weapon performance were going to take a level of great an increase in density? computing power that didn’t exist at the time but also that the We needed to put that quantitative information into our basic science pieces for building those computer calculations computer codes so they could accurately predict exactly were missing as well. when, during implosion, the subcritical pit would reach a One of the missing science pieces was an understanding of supercritical configuration needed to sustain a fission chain many of the properties of weapon materials—for example, reaction. But we didn’t have accurate experimental data to the strength and compressibility of many of the materials give us that quantitative information. Since we didn’t know within the “physics package” (the energy-producing part of this, we certainly couldn’t predict how decades of aging might the weapon, containing explosives and fissile material)—and change plutonium’s ability to compress. In fact, we didn’t even

The Los Alamos Plutonium Facility opened in 1978 to support nuclear weapons development and testing. After Rocky Flats was shut down in 1992, DOE tasked Los Alamos to begin pit manufacturing. The Los Alamos facility was the only one in the nuclear weapons complex that could be modified to do that kind of work. Compared with the 300,000 square feet at Rocky Flats, the Los alamos Plutonium Facility has only about 60,000 square feet of laboratory space in which Laboratory personnel can conduct almost all the plutonium science and all the pit production in the United States. (Photo: Los Alamos)

National Security Science July 2014 7 Another missing science piece was a detailed quantitative understanding of the other physical processes that go on during a nuclear detonation. (See “Nuclear Weapons 101.”)

Through experience and nuclear testing, these processes had been partially measured and modeled, but never to the degree that would make us confident that a bottom-up calculation would be predictive, that is, would provide an accurate picture of exactly how all the processes fit together into a working whole. To do the basic science experiments needed to improve our understanding of these processes and convert that understanding into mathematical models for high-resolution, 3D, bottom-up calculations of weapon performance, stewardship provided for a number of new research programs. It also provided for new facilities at Los Alamos, Lawrence Livermore, and Sandia National Laboratories. By the year 2000, DOE had established nearly a dozen “campaigns” to address these science issues. These campaigns have made tremendous progress in filling in the gaps in the myriad physics and materials issues of relevance to weapon assessment, and they continue to make advancements to this day.

Accelerated Strategic Computing Initiative

For stockpile stewardship, Los Alamos scientists use 3D computer visualiza- One important campaign was about investing in power- tions (like the one shown here) to understand the results of weapon ful new scientific computing capabilities—advanced, fast performance simulations. (Photo: Los Alamos) supercomputers and new computer codes—to perform the bottom-up calculations, which would include all the new fun- damental science and data from new experiments. In other know whether its compressibility, strength, and metallurgical words, we would take all the new data on material proper- stability actually would be affected by aging. So one of the ties, combine those data with the physics we learned, wrap first things we had to do in stewardship was build the tools all that into new weapons computer codes millions of lines and facilities needed for measuring these types of material long and developed over many years and have the codes step properties in plutonium and in other key weapon materials. through a detonation piece by piece. The codes would mock up the nuclear weapon virtually, first in two dimensions and During the implosion of a primary, ultimately in three, using millions of pixels to model the exact shapes of weapon components. And the codes would track a precise sequence of processes the changes in each pixel for many tiny increments of time to must work together perfectly. accurately simulate the detonation. In the mid-1990s, a full-system bottom-up calculation—from In 1997 I moved from the group that was charged with the detonation of high explosives to the final energy release examining pits and plutonium, and I asked to start a program of the entire warhead—would have had to run for years to to study aging in all the materials within the weapon. We reach completion at our newly desired levels of detail. We called this work “enhanced surveillance.” Initially, enhanced needed to reduce that running time from years to months, surveillance was a $7 million program at Los Alamos, but and we needed to do it as soon as possible because most of the within a few years, it grew to five times that size. By 1999 weapons designers with testing experience would be retiring we had 40 science projects at Los Alamos, and another 100 over the next decade or two. Their real-life testing experiences projects at other labs and sites, devoted to learning how the would be critical to evaluating the accuracy of the computer various materials would age and how that aging would affect models we hoped to generate. a weapon’s performance. Some of the country’s best chemists, engineers, and materials scientists became focused on aging nuclear weapons, and the success of their work formed a key basis for the Stockpile Stewardship Program.

8 Los Alamos National Laboratory At Nevada we built a state-of-the-art for stewardship, namely, facilities where weapons designers, old and new, could do integrated tests that reproduced some dynamic testing lab down in a mine. but not all aspects of weapon behavior. The real-world results from those integrated tests would provide a check on what the We were running to beat the clock, so Reis, working at DOE, codes predicted for the same phenomena. created ASCI, the Accelerated Strategic Computing Initiative. The most common integrated test today is, as it was in the Under that initiative, DOE and the computer industry began testing era, the hydrodynamic test, or “hydrotest,” a non- producing, at an accelerated pace, computational platforms nuclear test in which a replica of a primary undergoes implo- that started to break records in terms of their capabilities. For sion and the implosion is imaged by x-rays. These implosion example, we reached 1,000 trillion calculations per second experiments are called hydrodynamic tests because, at the (petaflops) in 2008 with the Roadrunner supercomputer, high pressures attained during implosion, the materials flow a milestone that was widely considered impossible in the like liquids. To keep the hydrotest nonnuclear, a surrogate 1990s. Another important advance was the move to parallel metal is used in place of plutonium. processing. Thousands of processors were now used to compute different parts of the same problem simultaneously. These advances increased computational power from millions Hydrotests at DARHT of calculations per second (megaflops) to trillions (teraflops) The most important integrated test facility at Los Alamos is and eventually quadrillions (petaflops) of calculations DARHT [pronounced “dart”], the Dual-Axis Radiographic per second. And all this was done to enable the massive Hydrodynamic Test facility (see p. 41). At DARHT the calculations that were needed for modeling a nuclear weapon. hydrotest of a mock primary occurs inside a sealed steel test vessel, and two powerful x-ray machines set at a 90-degree angle to each other take simultaneous x-rays of the implo- Integrated-Test Facilities sion process, giving us two views at one instant. One of the But it wasn’t enough to have the fundamental data in the new machines takes a single image, and the other captures a four- codes and to run the new codes on the new supercomputers. image sequence, thereby making a kind of a short “movie.” We also needed to validate the predictions from the new codes Continued on p. 11 as correct, so we brought to bear the third major investment

Down in a mine called U1a, at the Nevada National Security Site, two members of the Los Alamos staff prepare the front end of Cygnus, a powerful x-ray machine similar to DARHT. Two electron beams traverse the two parallel tubular sections (foreground and center) from right to left, are bent, and produce intense x-ray pulses behind the metal wall at the far left. The pulses emerge at a 60-degree angle to each other to record different views of an implosion experiment as in the Gemini experiments (p. 10). (Photo: Los Alamos)

National Security Science July 2014 9 Gemini Experiments

Revolutionary diagnostics at the U1a plutonium laboratory at the Nevada National Security Site (NNSS) have the potential to answer difficult questions about the aging of plutonium, pit manufacturing, features on a pit’s surface, and certification of reused pits. In that way, it is possible that they will save billions of dollars in pit production costs. Those diagnostics were in play during the recent Gemini experiments. Named after the constellation Gemini (the twin brothers Castor and Pollux in Greek mythology), the series consisted of twin hydrotests: scaled-down implosions that test material behavior in a condition similar to that of a weapon primary. The first test, Castor, was designed with a surrogate metal in place of plutonium. Pollux, which used plutonium, is referred to as a subcrit because it did not use enough plutonium to achieve a critical mass. The United States has used the NNSS to execute subcrits as part of stockpile stewardship since 1997. The idea of the Gemini series was to compare the implosion behavior of a surrogate with that of plutonium. The use of surrogate materials is highly desirable—for example, they are less expensive to use, and production is easier. Surrogates are routinely used within the Weapons Program, but we are still studying the limits of their applicability as representatives of plutonium in hydrotests and other experiments. To what extent can experimenting with surrogates tell us how well aged plutonium pits or pits made with new manufacturing processes implode? Do the data obtained from experiments with surrogates contain gaps that affect the data’s usefulness for validating the accuracy of the weapons codes? The Gemini experiments could help answer such questions. The two shots were phenomenally successful. “Diagnostic equipment fielded by our scientists resulted in more data of this kind collected in this single experiment [Pollux] than in all other previous subcritical experiments,” says NNSA Deputy Administrator for Defense Programs Don Cook. “In both Castor and Pollux, the new photon Doppler velocimetry (PDV) diagnostic tool used hundreds of laser beams to continuously monitor the velocity of hundreds of points on the imploding material—all recorded while the material was being driven inward by shock waves from high explosives. PDV produces 10,000 times more data than previous techniques. It is like going from the dots and dashes of the Morse code to high-definition TV. Simultaneously, Cygnus, a powerful x-ray machine (see photo, p. 9), took x-ray snapshots of the implosion from different angles. Used together, x-rays and PDV have the potential to detect effects from aging, processing changes, and features that could impact weapon performance.” Cook continues, “This type of data is critical for ensuring that our computer simulations can accurately predict performance and thus is critical for continuing our confidence in the safety and effectiveness of the nation’s stockpile.”

In PDV the novel fiber-optic probe shown here measures the velocity distribution of the surface of an imploding pit (not shown) by using hundreds of very thin laser beams. When each laser beam reflects off that surface, its frequency shifts in proportion to the surface velocity at that point. Those shifts made by the different beams thus become a continuous time record of the velocity distribution.

10 Los Alamos National Laboratory The proton radiography facility at the Los alamos Neutron Science Center, where a powerful proton beam can take “movie” images of a shock wave traveling through high explosives and other weapons materials. (Photo: Los Alamos)

Continued from p. 9 Over 20 years ago at the Nevada site, a shaft and its DARHT’s images have unprecedented resolution, and we supporting network of tunnels were dug 963 feet below the can compare them with our calculations to check whether desert surface. This complex, called U1a, was built to contain the calculations simulated the implosion correctly. These an underground nuclear test, but the test never took place. capabilities make DARHT a unique experimental facility Over the last15 years or so, U1a has been expanded and and critical to the stewardship program because having modernized into a highly sophisticated, unique laboratory integrated experimental data for direct comparison with with advanced diagnostics. Today, U1a is the only place in computer simulations is absolutely key to validating our the nation where high-explosives-driven plutonium testing codes and calculations. Lawrence Livermore also developed takes place. Cygnus (see photograph on p. 9), which is akin to an important integrated-testing tool at the same time—the a miniature version of DARHT, is an example of an advanced National Ignition Facility, NIF. While DARHT concentrates diagnostic at U1a. Cygnus takes x-ray pictures of plutonium on hydrodynamics in the implosion stage of a primary, NIF as it is explosively imploded. is used for studies of later elements of weapon function that Recently, in collaboration with National Security are also important to model and understand. DARHT and Technologies, we added photon Doppler velocimetry, PDV, NIF are used by scientists from each laboratory to gain new to our diagnostics. PDV uses hundreds of laser probe beams understandings of weapons performance and behavior. (see photo on opposite page) to provide substantially more and better data than previously possible, data that is used to DARHT is a unique experimental better understand the dynamic behavior of nuclear materials. facility and critical to the In essence, we built a state-of-the-art plutonium-testing laboratory in a mine, a lab that is revolutionizing our ability stewardship program. to understand and assess how nuclear weapons function. The recent Gemini experiments (see opposite page), which won Nevada National Security Site the prestigious Secretary of Energy Achievement Award, were Because we don’t use plutonium at DARHT, we needed to conducted at U1a. build a facility at the Nevada Test Site [now the Nevada National Security Site] where we could do integrated tests involving plutonium and high explosives. By both executive Proton Radiography and congressional order, such experiments would have to be DARHT’s x-rays let us take a sequence of four images of subcritical, “subcrits.” These are experiments that dynamically the implosion of a surrogate weapon primary. Because it compress plutonium with explosives but must never produce uses strong x-rays, DARHT is very good at imaging dense a critical mass. materials like metals. But many of a weapon’s materials (such

National Security Science July 2014 11 as explosives, foams, and cushions) aren’t dense; they’re Weapon Autopsies relatively lightweight. When DARHT is tuned to look for the An important element of stewardship is a surveillance movement of metals, it can’t easily image the movement of program to monitor the aging of weapons in the stockpile. shocks in things like high explosives. This problem has been Each year the Navy and Air Force return several weapons of known for many years, and some very clever scientists at Los each type. Most of these are nondestructively examined and Alamos figured out that protons—the nuclei of hydrogen returned to the military. A small number of these weapons atoms—would make an excellent probe to image these lighter undergo destructive evaluation. In essence, we perform materials. an autopsy on them. The weapon is disassembled into its Hence, the science of proton radiography, pRad, was born. components, and those components are sent back to their The pRad facility, an outgrowth of the Los Alamos Neutron production agencies for evaluation. Pits are returned to Los Science Center (LANSCE), uses protons to take images of Alamos, where we cut them open for detailed examination. many of the materials in the physics package at high contrast. Plutonium is extracted and subjected to a variety of tests Proton radiography is especially well suited to studies of the to look for aging or for birth defects [flaws created during movement of shock waves inside the explosives themselves. original manufacture]. These measurements are compared Very short pulses of protons, accelerated to over 80 percent with the manufacturing records for that specific unit, and of the speed of light, can penetrate these materials and changes are noted that may have resulted from aging. create a sequence of 10 or more 2D “movie” images of, say, a detonation travelling through high explosives at 17,000 miles per hour. Cold War weapons were much like Ferraris: complex and lightweight, with high performance but little margin for error.

During these surveillance operations, if we find a deviation from specifications, we report this as a Significant Finding Notification, or SFN. The designers evaluate each SFN, and if they feel it requires further assessment, they elevate the notification to a Significant Finding Investigation, or SFI. From 1995 to 2005, the three weapons laboratories opened and investigated a total of 156 SFIs. Of these 156 SFIs, 75 were determined to be “nonactionable.” In these 75 cases, the investigation and assessment revealed that no impact on safety, security, or performance was anticipated. The remaining 81 SFIs were deemed to be actionable, and a component or material was changed, often as part of a scheduled refurbishment process, or a change was made to the certification of the weapon, usually as a limitation in storage, deployment, or military requirements. Using the tools of stewardship and the expert judgment of laboratory staff, these SFIs are being closed. In FY 2013 three SFIs were closed, and to date one SFI has been closed in FY 2014.

Pit Manufacturing When the Department of Energy closed the Rocky Flats Plant, the facility had not completed enough W88 pits to support destructive surveillance activities. As a consequence, it became apparent that the nation needed to restore its ability to make more pits. That mission was assigned to Los Alamos by then secretary of energy Hazel O’Leary.

U.S. Air Force missileers prepare a Minuteman III intercontinental ballistic mis- sile for a test launch at Vandenberg Air Force Base in California. (Photo: U.S. Air Force)

12 Los Alamos National Laboratory This became the pit rebuild program, active from 1997 to complex, high performance, and lightweight, with little mar- 2010. In addition to resupplying pits for the Navy’s W88 gin for error and with costly build and maintenance require- warheads, pit rebuild had three other important goals. One ments. And it took not one nuclear test but in some cases up was to capture some of the manufacturing technologies to a dozen to confirm that the highly optimized designs would previously used at Rocky Flats and put them to use at work under all kinds of environmental and combat condi- the Lab’s Plutonium Facility. The second was to develop tions. We tweaked these designs between tests to ensure they replacement technologies for those processes that couldn’t be were operating as we intended, given their tiny margins for replicated. The third was to demonstrate that we could certify error. these newly rebuilt pits, along with certain new production Recall that during the Cold War we designed weapons to stay methods, using integrated experiments, simulations, and in the stockpile for 10 to maybe 20 years, certainly not 50 or other tools of stewardship. 70 . . . or 100 years. New production and new designs had always replaced older weapons in the stockpile. But all this Rebooting Aged Weapons changed with the period from 1989 to 1992. It is important to understand the design goals and charac- The result is that the age of our weapons today requires us teristics of the Cold War–era stockpile, the stockpile we still to eventually refurbish and “life extend” each warhead. This have today. Weapons designed during the Cold War placed refurbishment is the work of the life-extension programs a premium on military characteristics designed to deter a (LEPs). The LEPs are designed to refurbish, modify, update, specific adversary, the Soviet Union. One of the design goals or replace components to ensure that the weapons remain was to stretch limited plutonium inventories as far as possible safe, secure, and reliable for an additional 20 to 30 years. The in order to build the most weapons from the limited supply of LEPs were executed first for the W87 (a Livermore design) this strategic material. We were in an arms race with the Soviet and then for the W76 (a Los Alamos design). The B61 bomb Union, and every gram of plutonium mattered. If you could (also a Los Alamos design) LEP is now underway. Eventually, reduce the amount of plutonium in a weapon, you could build all the weapon types may be “rebooted” in this fashion. a few more weapons.

Optimizing yield to weight was everything. This didn’t come for free.

At the same time, we wanted to optimize the yield-to-weight ratio in warheads going onto missiles: we wanted the biggest yield for the least amount of plutonium and in the smallest and lightest warhead package. This allowed the nation to place multiple warheads on a single missile, expanding the target set and enhancing Cold War deterrence. This was especially true for warheads on strategic missiles, where weight was at an absolute premium. Optimizing yield to weight was everything in our designs. This didn’t come for free. The price we paid in optimizing lightweight designs for maximum yield was less margin for error and greater complexity—in some cases we made these warheads very complicated. The history of Cold War design at the national laboratories is one of exceptional success; we’re very proud of the fact that we did, indeed, build very lightweight, compact, and powerful nuclear weapons. These weapons helped end the Cold War. But we also didn’t leave much margin in the performance of these designs. The margin for error was quite low. In these designs, even something small going wrong can affect the weapon’s performance. We often compare weapon designs to sports cars. Cold War weapons were much like Ferraris:

Test launch of a Minuteman III intercontinental ballistic missile at Vandenberg Air Force Base in California. (Photo: Open Source)

National Security Science July 2014 13 The Silent Sentinels Some people say nuclear weapons aren’t that important any- more. In my mind nothing could be further from the truth. I recall a story from a few years ago. During a congressional hearing, a member of the military was asked, basically, what role nuclear weapons still had. Why did we still need them? The answer was, “Nuclear weapons function every day. They are our silent sentinels, reminding everyone of this country’s ultimate means of reprisal . . . . Those that would wish ill to the United States must always calculate, have second thoughts, when contemplating an act against us.” That’s deterrence. At a deep level, I don’t like the fact that we have to threaten retaliation to maintain peace. However, that’s the contradic- tion of deterrence. And from 1945 until today, it hasn’t failed. It still operates. Norris Bradbury [the Laboratory’s second director] used to call new staff members into his office for a short discussion. He would start by saying, “If the products of our work are ever again used in anger, then we will have failed in our mission. We don’t build nuclear weapons to kill people. We build nuclear weapons to buy time for our political leaders to find a better way.” Bradbury understood the contradiction Norris Bradbury, the Laboratory’s second director (Photo: Los Alamos) of nuclear weapons—that we retain these objects of awful destruction in order to preserve the ultimate peace. Nuclear weapons have a destructive power that current Los Alamos are not the sole protectors of our security. The generations have never witnessed. They’ve never seen a work itself—the science and engineering—is also part of the nuclear weapon tested; it’s only in the abstract that they can deterrent. Elements of this strategy, a capability-based deter- appreciate the awful power of these creations. Harold Agnew rent, have been adopted as part of the 2010 Nuclear Posture [the Laboratory’s third director] proposed that once in every Review conducted by the Obama administration. generation a nuclear weapon be detonated above ground, with world leaders required to witness it and see for them- selves its sheer size and power. If each generation of leaders We build nuclear weapons to buy did this, they would surely never use a nuclear weapon. time for our political leaders to find a better way. A Better Way The most important element of stockpile stewardship and a Is there a better way? Can we achieve the benefit of deter- capability-based deterrent is the people. I’ve been a witness rence while lessening the risks? These questions were a few to innovations that astound me to this day. The clever ideas, that I examined during my time at Stanford University. I dedication, and work ethic of Los Alamos staff are extraordi- came to understand that the work of Los Alamos and the nary. There have been achievements here in support of stew- other weapons laboratories was growing in importance as the ardship that the previous generation couldn’t have imagined. country and the world strove to reduce the sheer numbers My greatest pride comes from interacting with hundreds of of nuclear weapons. Indeed, could we find a roadmap to the exceptional scientists and engineers at the Laboratory. The vision Bradbury had of a better way? challenge in capability-based deterrence is ensuring an agile I’ve come to believe that as stewardship has moved forward, capability. We must be able to respond to world develop- there’s been a new kind of payoff. As we become really good ments with sufficient agility so that no one doubts our ability at understanding how nuclear weapons work and more to overwhelm and defeat an adversary. confident that we can, with agility, reconstitute an arsenal to In a very real sense, our deterrent will evolve so that it’s not respond to new threats, that capability itself becomes a grow- just the products of our work—the nuclear systems we design ing part of the deterrent. This is the future. Several prescient and maintain—but our work itself that will become the pro- Lab staff members predicted this many years ago. Ted Gold tector of our security. In this vision, the Laboratory is more and Rich Wagner, in consultation with John Immele, wrote important than it ever was, and that’s where we’re headed. a paper in 1990, “Long Shadows and Virtual Swords,” which ~Joseph Martz examined this strategy. The weapons that we designed at

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